Syringe pumps, diaphragm pumps, or peristaltic pumps usually are employed to precisely meter aggressive media. Depending on their construction, these pumps have disadvantages for certain applications. Syringe pumps are expensive due to the required electronic actuation and cannot deliver continuously. Peristaltic pumps and diaphragm pumps are too inaccurate for precise metering; in addition, diaphragm pumps only can deliver in one direction and cannot tightly close the medium against a backpressure.
However, there is already known a metering unit with which medium can be delivered in two directions, and which substantially consists of a fluid communication base, a pump, and two valves.
Such a metering unit is offered, for example, by the firm Bürkert as micrometering unit, type 7616. In this metering unit, the pump is arranged on one side of the fluid communication base, which cooperates with a pump chamber located on the same side of the fluid communication base. On the opposite side of the fluid communication base, the two valves are arranged. The pump is connected with the two valves via fluid passages, which extend through the fluid communication base from one side of the fluid communication base to the opposite side of the fluid communication base.